During the injection operation, the torque of the pump causes a delay of the pump mass with simultaneous elastic stressing of the drive shaft connection of the pump. After the injection operation, the pump mass is again accelerated under equalization of the stressing of the drive shaft connection. The problem with conventional arrangements is that when the flyweights reach the rotational velocity of the pump drive they are lifted off from the slide surfaces and abut the slide again during the next injection operation. This relieving of the surfaces sliding one on the other is desirable in order to achieve, along with small rotational speed changes, a movement of the flyweights along the slide surfaces and therewith a change of the injection start. Return springs oppose the lifting off, which are arranged between the two clutch parts and whose force is directed opposite the centrifugal force of the flyweights.
If one presupposes an existing pump mass and elasticity of the drive connection, then the negative torque acting back from the injection pump on the internal combustion engine is dependent on the magnitude of the torque necessary during the injection operation and on the magnitude of the injection pressure. When exceeding a predetermined injection pressure, the repeated lifting-off with corresponding re-impacting of the flyweights on the slide surfaces becomes so deleterious that the slide surfaces are destroyed after a relatively short time of operation.
It is possible to counteract the lifting off by an increase of the force of the return springs. This, however, reduces the useful working capacity of the timing device so that flyweights with greater mass and correspondingly with a larger structural volume are necessary for the timing device in order to obtain again the original working capacity.
Timing devices are known in which both the flyweights in the one clutch part as well a the slide members connected therewith are guided in corresponding grooves of the other clutch part. In these prior art timing devices the positive and also the negative torques are transmitted by abutment of the slide members and of the flyweights at the corresponding groove flanks. The manufacture of such timing devices, however, is relatively costly and curved grooves with slight clearance or play of the slide members for achieving predetermined injection characteristics can be realized only with difficulty.